In the course of dental treatment, it is often necessary or desirable to isolate oral tissue from a treatment area. This isolation may protect the isolated oral tissue from materials, such as caustic, acidic or abrasive materials, used during treatment. The isolation may also serve to maintain improved control over the treatment area by the reduction of oral fluids and to ensure a dry field, free of contaminates or other tissue.
In the past, cotton rolls, absorbent materials, or rubber dams and frameworks have been used to isolate dental tissues. These materials have been limited by their ability to achieve complete isolation of tissue directly adjacent to a treatment area. For example, cotton rolls or other absorbent material will absorb moisture or water rendering them of temporary benefit. A rubber dam framework does not work well in isolating the tissue nearest a treatment site and can be difficult to apply. A rubber dam is also not effective in isolating newly erupted teeth where clamping of a framework is not possible due to limited exposed hard tissue.
An alternative method to isolate dental tissues is to use polymerizable isolation barrier materials. In general, these materials are formulated with low molecular weight, difunctional monomers which generate hard, crosslinked structures when polymerized. Typically, monomers have molecular weights ranging from about 100 to 600. Currently available polymerizable isolation barrier materials are typically comprised of Bis-GMA (Bis phenol A glycidal methacrylate) and TEGDMA (tri-ethylene, glycol dimethacrylate) having low molecular weights of 512 and 286, respectively. When polymerized, these compounds or monomers react together hundreds or thousands of times before a completely set material is obtained. Fully reacted materials may contain polymers having molecular weights of one million or more.
The problems with the current polymerizable tissue barrier materials have been noted, e.g., in U.S. Pat. No. 6,086,370, and include, but are not limited to, the heat of polymerization causing a painful response from a patient, the cured material being too rigid making it difficult to remove from undercuts or situations where the materials can interlock within tooth structures, the material prior to curing being of low viscosity causing the material to run or displace from its original position, and the material not adhering well to tissue making accurate placement of these materials difficult.
Previous attempts have been made to alleviate these problems. In U.S. Pat. No. 6,086,370, reflective substances were incorporated within the barrier material in an attempt to reduce the amount of light absorbed during curing and thus change the rate of polymerization and/or heat of polymerization. Tissue adherence substances, such as gums, cellulose, or polyols were also incorporated within the barrier material in order to improve tissue adherence. However, the amount of heat generated during curing and the tissue adherence may still be improved.
Significant amounts of filler material are often added to render the barrier materials more viscous or less flowable. However, high amounts of fillers impart undesirable rigidity to these materials. A rigid, non-pliable material is difficult to remove from certain areas, such as an undercut, and may pinch adjacent tissues, causing patient discomfort. The removal of rigid, non-flexible material may necessitate the use of dental cutting instruments, which can damage adjacent tooth structures. A flexible material that is easy to bend may be easily removed from between teeth or from an undercut. Such a pliable material elongates or deforms to allow easy removal.
Some tissue barrier materials are supplied in colors, such as blue or green, to provide good contrast to oral tissue colors such as white (tooth) or red (gingival). However, such colored formulations tend to increase the heat generated in the material during curing due to light absorption. A limitation of white, reflective materials is the lack of contrast with tooth-like colors. This limitation may be important where the tissue barrier material is used in bleaching or tooth whitening. A color contrasting the original or final tooth shade is beneficial to identify the tooth color and to distinguish the tissue barrier material.
Due to the heat generated during the curing of barrier materials, dentists are often instructed to limit the patient discomfort by curing the material for only 1–2 seconds at a time. Typically, these materials require 10–20 seconds of intense light exposure to one applied area by an appropriate light curing source to cure completely. A material with a lower heat of polymerization enables the barrier material to be continuously cured and provides a quicker, more efficient process.